On 1/31/23 15:16, Simon Glass wrote:
Hi,
On Tue, 31 Jan 2023 at 05:04, Ilias Apalodimas
<ilias.apalodi...@linaro.org> wrote:
Hi all,
On Mon, Jan 30, 2023 at 01:30:49PM -0500, Tom Rini wrote:
On Mon, Jan 30, 2023 at 01:13:55PM -0500, Tom Rini wrote:
On Sat, Jan 28, 2023 at 09:57:45AM +0100, Heinrich Schuchardt wrote:
<snip />
I thought we had rejected going down this path since the UEFI spec is
unhelpfully wrong if it insists this?
Because, to be clear, stopping hardware watchdogs is not to be done. The
one in-tree caller of wdt_stop_all is very questionable. You cannot
seriously stop a watchdog until someone else can hopefully resume it as
that violates the function of a hardware watchdog. A pure software
watchdog is one thing, and a hardware watchdog is another. I feel like
the most likely answer here is that someone needs to, still, push back
to the UEFI specification to get hardware watchdogs better understood
and handled, as it must never be stopped once started and if you cannot
reach the next stage in time, that's an engineering issue to resolve. My
first guess is that ExitBootServices should service the watchdog one
last time to ensure the largest window of time for the OS to take over
servicing of the watchdog.
There's two scenarios I can think of
1. After U-Boot is done it can disable the hardware watchdog.
The kernel will go through the EFI-stub -> kernel proper -> watchdog
gets re-initialized. In that case you are *hoping* that device won't
hang in the efi-stub or until the wd is up again.
2. EFI makes sure the hardware wd gets configured with the highest allowed
value. The efi-stub doesn't have any driver to refresh the wd, so we
will again rely on the wd driver coming up and refreshing the timers.
None of those is perfect, but I prefer the latter
How does this work if U-Boot runs grub instead of Linux? Does grub
update the watchdog?
U-Boot will reset the watchdog when the UEFI API is invoked to read the
console or to access the network or block devices. Just grep for
"efi_timer_check()".
Best regards
Heinrich
